Electrolytic treatment method and apparatus, and method and apparatus for manufacturing planographic printing plate

ABSTRACT

An electrolytic treatment apparatus according to one aspect of the subject matter includes: a transportation device configured to transport a metal plate; an electrolytic bath configured to store an acidic electrolytic solution, wherein the metal plate is transported inside the electrolytic bath; a current supplying device configured to supply an alternating waveform current to continuously subject a surface of the metal plate to an alternating current electrolytic treatment with the alternating waveform current; and a hydroxide ion-adding device installed in an inlet of the electrolytic bath through which the metal plate is introduced into the electrolytic bath, the hydroxide ion-adding device configured to add hydroxide ions (OH − ) on a surface of the metal plate before the surface of the metal plate is subjected to the alternating current electrolytic treatment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The presently disclosed subject matter relates to an electrolytic treatment method and apparatus, and a method and an apparatus for manufacturing a planographic printing plate, and particularly to an electrolytic treatment method and apparatus which can effectively suppress the generation of chatter marks when a continuous aluminum plate is electrolytically surface-roughened, and a method and an apparatus for manufacturing a planographic printing plate.

2. Description of the Related Art

A planographic printing original plate as an original plate of a planographic printing plate is generally manufactured according to procedures in which a surface of a plate of pure aluminum or an aluminum alloy (hereinafter, referred to as “aluminum and the like” in some cases) is roughened, and then subjected to an anodizing treatment to manufacture a support for a planographic printing plate, and in which a photosensitive resin or a thermosensitive resin is applied on the support for a planographic printing plate to form a photosensitive or thermosensitive plate making layer.

In such a manufacturing process of a planographic printing original plate, an aluminum web as a long aluminum plate is surface-roughened by a mechanical surface-roughening treatment using a brush roller, a grinding roller or the like, an etching treatment involving chemical surface-roughening using an alkali, an electrolytic surface-roughening treatment involving an electrolytic treatment using the aluminum web as one of electrodes, and the like.

Since the electrolytic surface-roughening treatment is usually carried out by applying an alternating waveform current, such as a sinusoidal wave current, a rectangular wave current or a trapezoidal wave current, to an aluminum web in an acidic electrolytic solution, a positive voltage and a negative voltage are alternately applied to the aluminum web in an inlet of an electrolytic bath.

An anodic reaction occurs when a positive voltage is applied to the aluminum web; and a cathodic reaction occurs when a negative voltage is applied to the aluminum web. In a cathodic reaction, hydroxide ions are produced and reacted with aluminum ions in a solution to thereby produce deposits (precipitations) composed of aluminum hydroxide as a main component. In an anodic reaction, an oxide film is produced and defect portions of the film dissolve to thereby produce beehive-like small holes called pits.

Therefore, an aluminum web passing through an electrolytic bath is first subjected to an anodic reaction when a positive voltage is applied in the inlet of the electrolytic bath, and to a cathodic reaction when a negative voltage is applied. Then, among the beehive-like small holes, holes nonuniform in size are liable to be formed on the aluminum web surface if the alternating current electrolytic treatment is initiated from an anodic reaction; and holes uniform in size are easily formed if the alternating current electrolytic treatment is initiated from a cathodic reaction.

Thus, the surface condition of an aluminum web varies depending on the polarity of a current applied in an inlet of an electrolytic bath. That is, since the surface conditions are different between portions where an alternating current electrolytic treatment is initiated from an anodic reaction and portions where the alternating current electrolytic treatment is initiated from a cathodic reaction, stripe-like unevenness of light and shade where portions 1 looking dark and portions 2 looking light emerge alternately at intervals of about 1 cm in the transportation direction of an aluminum web, that is, chatter marks are sometimes produced on the aluminum web surface as illustrated in FIG. 6. FIG. 6 illustrates the light and shade in exaggeration in order to describe chatter marks.

Japanese Patent Application Laid-Open No. 2003-003299 and Japanese Patent Application Laid-Open No. 2007-270217 disclose solutions to these problems. Japanese Patent Application Laid-Open No. 2003-003299 discloses an electrolytic treatment apparatus in which in an inlet of an electrolytic bath, a soft start part to electrolytically treat at a lower current density than that in an alternating waveform applied inside the electrolytic bath is provided.

Japanese Patent Application Laid-Open No. 2007-270217 contends that an alternating current electrolytic treatment after an oxide film is previously formed on a metal plate surface by an anodic reaction can suppress chatter marks.

SUMMARY OF THE INVENTION

However, Japanese Patent Application Laid-Open No. 2003-003299 and Japanese Patent Application Laid-Open No. 2007-270217 can not suppress the generation of chatter marks sufficiently. In the case of Japanese Patent Application Laid-Open No. 2007-270217, a suitable thickness of the oxide film formed on a metal plate surface is in the range of 0.1 to 1 μm. If the thickness is larger than that, holes are hardly formed by an anodic reaction in an alternating current electrolytic treatment, and the surface condition thereby becomes much different from a target surface condition. Therefore, in order to make the thickness of the oxide film suitable, there also arise a need for making the current density low and a problem of difficulty in control.

The presently disclosed subject matter has been achieved in consideration of such situations, and has an object to provide an electrolytic treatment method and apparatus which can effectively suppress the generation of chatter marks when a strip-shaped metal plate is continuously subjected to an alternating current electrolytic treatment with an alternating waveform current in an acidic electrolytic solution while being transported therein, and a method and an apparatus for manufacturing a planographic printing plate.

In order to achieve the above-mentioned object, the electrolytic treatment method according to the first aspect of the presently disclosed subject matter includes: continuously subjecting a strip-shaped metal plate to an alternating current electrolytic treatment with an alternating waveform current in an acidic electrolytic solution while transporting the metal plate therein; and before the alternating current electrolytic treatment, carrying out a pretreatment step of previously distributing (adding) hydroxide ions (OH⁻) on a surface of the metal plate.

The first aspect of the presently disclosed subject matter includes a pretreatment step of previously distributing (adding) hydroxide ions (OH⁻) on a surface of a metal plate before an alternating current electrolytic treatment step. Thereby, even for portions where the alternating current electrolytic treatment for the metal plate is initiated from an anodic reaction, hydroxide ions distribute on the metal surface to thereby allow suppression of the anodic reaction. Thereby, holes nonuniform in size are hardly formed on the surface of the metal plate, which gives holes at nearly the same level (nearly the same size) as those of portions where the alternating current electrolytic treatment is initiated from a cathodic reaction. As a result, since the size of holes of an aluminum web is uniformized, the generation of chatter marks can sufficiently be suppressed.

In the electrolytic treatment method according to the presently disclosed subject matter, the hydroxide ions are preferably formed by applying a negative direct-current voltage to the metal plate at an inter-electrode distance of 5 to 15 mm to carry out a cathodic reaction in an electrolytic bath in which the alternating current electrolytic treatment step is carried out (the second aspect of the presently disclosed subject matter).

Since hydroxide ions can be generated by applying a negative direct-current voltage to a metal plate to carry out a cathodic reaction, when the strip-shaped metal plate is continuously subjected to an electrolytic treatment with an alternating waveform current in an acidic electrolytic solution while being transported therein, the generation of chatter marks can effectively be suppressed even if the initiation reaction of the alternating current electrolytic treatment is different.

In this case, it is important to carry out the pretreatment step in an electrolytic bath for the alternating current electrolytic treatment step. Thereby, since the metal plate is never exposed in the air, hydroxide ions having been adhered on the metal plate surface on purpose can be prevented from diffusing into the air.

If the inter-electrode distance is longer than 15 mm, generated hydroxide ions diffuse in an electrolytic solution, so that hydroxide ions cannot be distributed sufficiently on a metal plate surface. Thereby, since the amount of hydroxide ions adhered on the metal plate surface becomes small, the suppressing effect on chatter marks cannot sufficiently be exhibited. If an attempt is made to sufficiently distribute hydroxide ions on the metal plate surface with the inter-electrode distance longer than 15 mm, a large current density is needed, resulting in an energy loss. Application of a positive voltage to an aluminum web causes a cathodic reaction; and application of a negative voltage thereto causes an anodic reaction. In the cathodic reaction, an oxide film composed of aluminum hydroxide as a main component is produced; and in the anodic reaction, the oxide film dissolves to produce beehive-like small holes called pits.

By contrast, if the inter-electrode distance is shorter than 5 mm, a direct current generation unit to apply a negative voltage to make a direct current flow has a risk of contacting with a metal plate being transported.

The presently disclosed subject matter may involve any method as long as the method is one in which hydroxide ions (OH⁻) can be previously distributed on a metal plate surface. However, as long as the method is one in which a direct current is made to flow by applying a negative direct-current voltage to a metal plate, a simple modification of an existing apparatus can meet the method.

In the electrolytic treatment method of the presently disclosed subject matter, the current density of the cathodic reaction is preferably −10 A/dm² or lower (the third aspect of the presently disclosed subject matter), more preferably −30 A/dm² or lower, and especially preferably −50 A/dm² or lower. Here, although the current density is expressed as “−10 A/dm² or lower” since the voltage is a negative direct-current voltage, the absolute value of the current density is preferably a larger one.

In the electrolytic treatment method of the presently disclosed subject matter, the current density of −10 A/dm² or lower exhibits a large suppressing effect on the generation of chatter marks, and a low current density of −10 A/dm² or higher makes the control unstable.

In the electrolytic treatment method of the presently disclosed subject matter, a time interval from at an end of the pretreatment step to at a start of the alternating current electrolytic treatment is preferably 5 sec or less (the fourth aspect of the presently disclosed subject matter). This is because if the time from the completion of the pretreatment step to the initiation of the alternating current electrolytic treatment step is too long, hydroxide ions present on the metal plate surface diffuse, so that a suppressing effect on the anodic reaction is lost. A more preferable time thereof is 1 sec or less, and an especially preferable time thereof is 0.1 sec or less.

In order to achieve the above-mentioned object, the electrolytic treatment apparatus according to the fifth aspect of the presently disclosed subject matter includes: a transportation device configured to transport a metal plate; an electrolytic bath configured to store an acidic electrolytic solution, wherein the metal plate is transported inside the electrolytic bath; a current supplying device configured to supply an alternating waveform current to continuously subject a surface of the metal plate to an alternating current electrolytic treatment with the alternating waveform current; and a hydroxide ion-adding device installed in an inlet of the electrolytic bath through which the metal plate is introduced into the electrolytic bath, the hydroxide ion-adding device configured to add hydroxide ions (OH⁻) on a surface of the metal plate before the surface of the metal plate is subjected to the alternating current electrolytic treatment.

The fifth aspect of the presently disclosed subject matter is a constitution as an apparatus for the electrolytic treatment according to the presently disclosed subject matter.

In the electrolytic treatment apparatus of the presently disclosed subject matter, the hydroxide ion-adding device is preferably a direct current unit installed in the electrolytic bath and at an inter-electrode distance of 5 to 15 mm from the metal plate, and applying a negative direct-current voltage to the metal plate (the sixth aspect of the presently disclosed subject matter).

In order to achieve the above-mentioned object, the method for manufacturing a planographic printing plate according to the seventh aspect of the presently disclosed subject matter includes, in the method for manufacturing a planographic printing plate having an electrolytic surface-roughening treatment step of electrolytically surface-roughening an aluminum plate, using an electrolytic treatment method according to any one of the first to fourth aspects of the presently disclosed subject matter for the electrolytic surface-roughening treatment step.

Since the electrolytic treatment method according to the presently disclosed subject matter is used for the electrolytic surface-roughening treatment in the manufacturing method of a planographic printing plate, the generation of chatter marks can effectively be suppressed. Provided that the aluminum plate involves aluminum alloy plates.

In order to achieve the above-mentioned object, the apparatus for manufacturing a planographic printing plate according to the eighth aspect of the presently disclosed subject matter includes, in the apparatus for manufacturing a planographic printing plate having an electrolytic surface-roughening treatment apparatus to electrolytically surface-roughen an aluminum plate, using an electrolytic treatment apparatus according to the fifth or sixth aspect of the presently disclosed subject matter for the electrolytic surface-roughening treatment step.

The eighth aspect of the presently disclosed subject matter is a constitution as an apparatus for manufacture of the planographic printing plate according to the presently disclosed subject matter.

According to the presently disclosed subject matter, when a strip-shaped metal plate is continuously subjected to an alternating current electrolytic treatment with an alternating waveform current in an acidic electrolytic solution while being transported therein, holes substantially uniform in size can be formed at portions where the alternating current electrolytic treatment is initiated from an anodic reaction, which gives holes at nearly the same level as those of portions where the alternating current electrolytic treatment is initiated from a cathodic reaction. As a result, the generation of chatter marks can effectively be suppressed.

Therefore, the application of the electrolytic treatment method and apparatus according to the presently disclosed subject matter to a method and an apparatus for manufacturing a planographic printing plate can carry out a high-quality surface-roughening treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional diagram illustrating one example of an electrolytic surface-roughening treatment apparatus equipped with a radial-type alternating current electrolytic bath according to an embodiment of the presently disclosed subject matter;

FIG. 2 is a schematic diagram illustrating a distribution of hydroxide ions on an aluminum plate surface;

FIG. 3 is a schematic diagram (cross-sectional view) of small holes formed on an aluminum plate surface in the case where an alternating current electrolytic treatment is initiated from an anodic reaction;

FIG. 4 is a schematic diagram (cross-sectional view) of small holes formed on an aluminum plate surface in the case where the alternating current electrolytic treatment is initiated from a cathodic reaction;

FIG. 5 is a table describing Working Examples of the presently disclosed subject matter; and

FIG. 6 is a schematic diagram (plan view) illustrating chatter marks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the electrolytic treatment method and apparatus, and the method and apparatus for manufacturing a planographic printing plate according to the presently disclosed subject matter will be described by way of accompanying drawings.

In the present embodiment, hereinafter described is one example of an application of the presently disclosed subject matter to a radial-type electrolytic surface-roughening treatment apparatus among electrolytic surface-roughening treatment apparatuses which subject an aluminum web as a continuous strip-shaped aluminum plate to an alternating current electrolysis to carry out an electrolytic surface-roughening treatment on the aluminum web.

FIG. 1 illustrates a sectional schematic diagram of one example of an electrolytic surface-roughening treatment apparatus equipped with a radial-type alternating current electrolytic bath suitably used in the presently disclosed subject matter.

As illustrated in FIG. 1, an electrolytic surface-roughening treatment apparatus 10 includes an electrolytic bath body 12 having an electrolytic bath 12A for storing an acidic electrolytic solution installed therein, and a feed roller 14 which is disposed in the electrolytic bath 12A and rotatably about an axis line extending in the horizontal direction and feeds an aluminum web W as a strip-shaped continuous thin plate to the direction of the arrow a, that is, from the right side toward the left side in FIG. 1.

The inner wall surface of the electrolytic bath 12A is formed in a nearly cylindrical shape so as to surround the feed roller 14, and semicylindrical electrodes 16A and 16B are installed on the inner wall surface of the electrolytic bath 12A, interposing the feed roller 14. The electrodes 16A and 16B are divided into a plurality of small electrodes 18A and 18B, respectively, along the circumferential direction, and insulating layers 20A and 20B are interposed between the small electrodes 18A and between the small electrodes 18B, respectively. The small electrodes 18A and 18B can be formed of, for example, graphite or a metal; and the insulating layers 20A and 20B can be formed of, for example, a vinyl chloride resin. The thickness of the insulating layers 20A and 20B is preferably 1 to 10 mm. In either of the electrodes 16A and 16B, the small electrodes 18A and 18B are connected to a power source AC, respectively. Any of the small electrodes 18A and 18B and the insulating layers 20A and 20B are held by an insulating electrode holder 20C to form the electrodes 16A and 16B.

The power source AC has a function of supplying an alternating waveform current to the electrodes 16A and 16B. The power source AC includes a sinusoidal wave generating circuit to generate a sinusoidal wave by regulating the current/voltage of a commercial alternating current by using an induction voltage regulator and a transformer, and a thyristor circuit to generate a trapezoidal wave current or a rectangular wave current from a direct current obtained by a device rectifying a commercial alternating current or otherwise.

An opening 12B is formed in the upper part of the electrolytic bath 12A. The aluminum web W, which is one example of the metal plate according to the present embodiment and is a continuous strip-shaped aluminum plate, is introduced and led out through the opening 12B, in an alternating current electrolytic surface-roughening treatment. An acidic electrolytic solution replenishing flow channel 22 to replenish an acidic electrolytic solution to the electrolytic bath 12A is installed in the vicinity of the downstream-side end of the electrode 16B in the opening 12B. Such an acidic electrolytic solution usable is a nitric acid solution, a hydrochloric acid solution or the like.

A group of upstream-side guiding rollers 24A to guide the aluminum web W inside the electrolytic bath 12A and a downstream-side guiding roller 24B to guide the aluminum web W subjected to surface-roughening treatment inside the electrolytic bath 12A, outside the electrolytic bath 12A are disposed in the vicinity of the opening 12B in the upper part of the electrolytic bath 12A.

An overflow tank 12C is installed on the upstream side of the electrolytic bath 12A in the electrolytic bath body 12. The overflow tank 12C has a function of temporarily storing the acidic electrolytic solution having overflowed from the electrolytic bath 12A for a while and holding the liquid level of the electrolytic bath 12A at a constant level.

In the electrolytic solution in the vicinity of an inlet for guiding the aluminum web W inside the electrolytic bath 12A, a direct current unit 26 to impart a negative direct-current voltage to the aluminum web W is installed at a position of 5 to 15 mm from the surface of the aluminum web W. The direct current unit 26 has a function of always causing a direct current to flow to the aluminum web W by applying a negative direct-current voltage to the aluminum web W in the inlet inside the electrolytic bath 12A.

An auxiliary electrolytic bath 28 is installed on the downstream side of the electrolytic bath 12A in the electrolytic bath body 12. The auxiliary electrolytic bath 28 is shallower than the electrolytic bath 12A, and has a bottom surface 28 A formed in a planar shape. A plurality of cylindrical auxiliary electrodes 29 is installed on the bottom surface 28A.

The auxiliary electrodes 29 are preferably formed from a highly-anticorrosive metal such as platinum, or a ferrite, and may be in a plate form.

The auxiliary electrode 29 are connected to a side of the alternating current power source AC to which the electrode 16A is connected, parallelly with the electrode 16A. A thyristor Th1 is connected between the auxiliary electrode 29 and the alternating current power source AC so that a current is made to flow from the side of the alternating current power source AC to which the electrode 16A is connected toward the auxiliary electrodes 29 at the ignition.

A side of the alternating current power source AC to which the electrode 16B is connected is also connected to the auxiliary electrodes 29 through a thyristor Th2. The thyristor Th2 is connected so that a current is made to flow from the side of the alternating current power source AC to which the electrode 16B is connected toward the auxiliary electrodes 29 at the ignition.

When either of the thyristors Th1 and Th2 is ignited, an anodic current flows through the auxiliary electrodes 29. Therefore, the phase-control of the thyristors Th1 and Th2 can control the current value of the anodic current flowing through the auxiliary electrodes 29, and can control also the ratio Qc/Qa of the electric quantity Qc flowing when the aluminum web W is cathodic to the electric quantity Qa flowing when anodic.

The auxiliary electrodes 29 and the direct current unit 26 are connected through a direct current power source.

The frequency of the alternating current is not especially limited, but is preferably 40 to 120 Hz, more preferably 40 to 80 Hz, and still more preferably 50 to 60 Hz.

The ratio Qc/Qa of the electric quantity Qc flowing in the aluminum web W in a cathodic reaction to the electric quantity Qa flowing therein in an anodic reaction is preferably 0.9 to 1, and more preferably 0.95 to 0.99. Thereby, uniform honeycomb pits can be formed on the surface of the aluminum web W.

The duty of the alternating current is not especially limited, but is preferably 0.33 to 0.66, more preferably 0.4 to 0.6, and most preferably 0.5, from the viewpoint of carrying out a uniform surface-roughening treatment on the surface of the aluminum web W and the viewpoint of manufacture of a power source apparatus. Here, “duty” in the present embodiment refers to ta/T where T represents a period of an alternating current, and to represents a time (anodic reaction time) during which an aluminum alloy plate is subjected to an anodic reaction.

The time TP until the current value of an alternating current reaches a positive or negative peak from zero is, in the case of a trapezoidal wave current, preferably 0.5 to 6 msec, and more preferably 0.6 to 5 msec. Thereby, more uniform crater-like concavities (pits) can be formed on the surface of the aluminum web W.

The electric quantity from the starting time to the finishing time in an electrolytic surface-roughening treatment as the sum total of the electric quantity when the aluminum web W is anodic is preferably 10 to 1,000 C/dm², more preferably 10 to 800 C/dm², and still more preferably 40 to 500 C/dm².

The current Iap at the peak time on the anode-cycle side in an alternating current and the current Icp at the peak time on the cathode-cycle side therein are preferably each 10 to 100 A/dm², more preferably 20 to 80 A/dm², and still more preferably 30 to 60 A/dm². Icp/Iap is preferably 0.9 to 1.5, and more preferably 0.9 to 1.0.

In an electrolytic surface-roughening treatment, in one or two or more electrolytic baths, a suspending period during which an alternating current does not flow through the aluminum web W is provided once or more times, and the suspending period is set at 0.001 to 0.6 sec, which is preferable because honeycomb pits are formed uniformly on the whole surface of the aluminum web W.

Hereinafter, the action of the electrolytic surface-roughening treatment apparatus 10 in the present embodiment will be described.

The aluminum web W guided from the right side to the electrolytic bath body 12A in FIG. 1 is first guided inside the electrolytic bath 12A by the upstream-side guiding roller 24A.

The aluminum web W guided inside the electrolytic bath 12A is first passed by the direct current unit 26. At this time, the direct current unit 26 applies a negative direct-current voltage to the aluminum web W to cause a cathodic reaction on the aluminum web W. Thereby, as illustrated in FIG. 2, a large number of hydroxide ions (OH⁻) are generated on a surface of the aluminum web W facing the direct current unit 26, and are distributed (added) on the surface of the aluminum web W.

After the aluminum web W having hydroxide ions distributed on the surface thereof is passed by the direct current unit 26, the aluminum web W is transported along the electrode 16A, and subjected to an alternating current electrolysis with an alternating waveform current applied to the electrode 16A by the power source AC. That is, a surface of the aluminum web W facing the electrode 16A is subjected to an alternating current electrolysis in which an anodic reaction and a cathodic reaction are alternately carried out. It is undecided whether the alternating current electrolysis is initiated from an anodic reaction or a cathodic reaction.

The anodic reaction in an alternating current electrolysis is, as described in Formula 1, a reaction in which aluminum dissolves to produce aluminum ions (Al³⁺) and electrons (e).

[Anodic reaction] Al→Al³⁺+3e⁻  Formula 1

The cathodic reaction in the alternating current electrolysis is, as described in Formula 2, a reaction in which hydrogen ions (H⁺) and electrons (e⁻) generate hydrogen gas. Hence, hydroxide ions (OH⁻) are produced on a surface of an aluminum web W, and as described in Formula 3, react with aluminum ions (Al³⁺) to produce a hydroxide (Al(OH)₃).

[Cathodic reaction] 2H⁺+2e→H₂  Formula 2

Al³⁺+3OH⁻→Al(OH)₃  Formula 3

Then, FIG. 3 illustrates a surface condition of a portion of an aluminum web W where an alternating current electrolytic treatment is initiated from an anodic reaction in the state that hydroxide ions are not distributed on the surface of the aluminum web W. As is clear from FIG. 3, the sizes of holes are nonuniform. By contrast, FIG. 4 illustrates a surface condition of a portion of an aluminum web W where an alternating current electrolytic treatment is initiated from a cathodic reaction, that is, a portion thereof where an alternating current electrolytic treatment is initiated from the state that hydroxide ions are distributed on the surface of the aluminum web W. As is clear from FIG. 4, the sizes of holes are uniform. Due to a difference between these surface shapes, a portion looking dark and a portion looking light when light strikes the portions are alternately formed in the direction in which the aluminum web is transported, that is, so-called chatter marks develop.

However, if hydroxide ions have been made to be distributed on a surface of an aluminum web W before the continuous electrolytic treatment with an alternating waveform current, as in the presently disclosed subject matter, even in the case where the alternating current electrolytic treatment is initiated from an anodic reaction, since the anodic reaction is suppressed by the hydroxide ions, the sizes of holes formed on the surface of the aluminum web W can be uniformized. Thereby, the development of chatter marks can effectively be suppressed.

Important points at this time, as described above, are to generate hydroxide ions inside the electrolytic bath 12A in which the alternating current electrolysis is carried out, and to set the inter-electrode distance L between the surface of the aluminum web W and the direct current unit 26 in the range of 5 to 15 mm.

By making hydroxide ions generated inside the electrolytic bath body 12A, since the aluminum web W is never exposed in the air, the hydroxide ions having been adhered on the surface of the aluminum web W on purpose are prevented from diffusing into the air.

If the inter-electrode distance L is longer than 15 mm, since generated hydroxide ions diffuse in the electrolytic solution, hydroxide ions cannot be distributed sufficiently on the surface of the aluminum web W. Hence, since the amount of hydroxide ions adhered on the surface of the aluminum web W becomes small, the effect on suppressing the generation of chatter marks cannot be exhibited. Further, if an attempt is made to sufficiently distribute hydroxide ions on the metal plate surface with the inter-electrode distance L longer than 15 mm, a large current density is needed, resulting in an energy loss.

By contrast, if the inter-electrode distance L is shorter than 5 mm, there arises a risk that the direct current unit 26 to apply a negative voltage to make a direct current flow contacts with the aluminum web W being transported.

The current density of the current flowing from the direct current unit 26 to the aluminum web W is preferably −10 A/dm² or lower, more preferably −30 A/dm² or lower, and especially preferably −50 A/dm² or lower. If the current density is −10 A/dm² or lower, the effect on suppressing the generation of chatter marks is exhibited, but a lower current density (a larger absolute value) makes the chatter mark-suppressing effect larger, and makes the control of the current density easier.

As described hitherto, in the electrolytic surface-roughening treatment apparatus 10 according to the present embodiment, since a pretreatment in which hydroxide ions (OH⁻) are previously made to be distributed on a surface of an aluminum web W is designed to be carried out before an electrolytic treatment step is carried out, when the aluminum web W is continuously subjected to an electrolytic treatment with an alternating waveform current in an acidic electrolytic solution while being transported therein, holes uniform in size can be formed on portions of the aluminum web W where the alternating current treatment is initiated from an anodic reaction, whereby the generation of chatter marks can effectively be suppressed.

The electrolytic surface-roughening treatment apparatus 10 in the present embodiment has further a feature that it can be remodeled inexpensively from a conventional electrolytic surface-roughening treatment apparatus because few components are needed to be newly added to the conventional electrolytic surface-roughening treatment apparatus.

In the present embodiment, the direct current unit 26 to apply a negative direct-current voltage to the aluminum web W is installed to generate hydroxide ions, but any method can be applied as long as the method can previously distribute hydroxide ions (OH⁻) on the surface of the aluminum web W. For example, water is electrolyzed in a separate apparatus to produce hydroxide ions, and the water containing hydroxide ions may be designed to be brought into contact with the surface of the aluminum web W right before the alternating current electrolytic treatment.

Hereinafter, as an example of an application of the electrolytic treatment method and apparatus according to the presently disclosed subject matter, a method for manufacturing a planographic printing plate will be described.

<Aluminum Web (Rolled (Milled) Aluminum)>

An aluminum plate used as the aluminum web W according to the present embodiment is a dimensionally stable metal containing aluminum as a main component. The aluminum plate involves aluminum alloy plates as described before, and hereinafter, these are generically referred to as aluminum plates.

As the aluminum plate, a plastic film or a paper on which an aluminum alloy is laminated or vapor-deposited may be used. Further, a composite sheet may be used in which an aluminum sheet is bonded on a polyethylene terephthalate film as described in Japanese Examined Application Publication No. 48-18327. The aluminum plate may contain elements such as Bi and Ni, and inevitable impurities.

As the materials of the aluminum plate, suitably utilizable are, for example, JIS A1050, JIS A1100, JIS A3003, JIS A3004 and JIS A3005 (non-ferrous metal materials (alloys) defined in Japanese Industrial Standards (JIS)), and the international registered alloy No. 3103A.

A manufacturing method of an aluminum plate may be either of a continuous casting system and a DC casting system, and an aluminum plate in which the process annealing and the soaking treatment in the DC casting system have been omitted may be used also. An aluminum plate may be used in which irregularities (concavity and convexity) are given by the pack rolling, the transcription or the like in the final rolling. The aluminum plate may be an aluminum web as a continuous strip-shaped sheet material or plate material, or may be a single sheet cut into a size corresponding to a planographic printing original plate shipped as a product, or another size.

The thickness of the aluminum plate is usually about 0.05 to 1 mm, and preferably 0.1 mm to 0.5 mm. The thickness can suitably be changed depending on the size of a printing machine, the size of a printing plate, and demands of users.

In the manufacturing method of a planographic printing original plate of the present embodiment, the planographic printing original plate is obtained by subjecting various types of surface treatments including the electrolytic surface-roughening treatment in an acidic aqueous solution to the aluminum plate, but the various types of surface treatments may contain additionally various types of treatments.

Before the electrolytic surface-roughening treatment, an alkali etching treatment or a desmutting treatment is preferably carried out, and the alkali etching treatment and the desmutting treatment may also be preferably carried out in this order. After the electrolytic surface-roughening treatment, an alkali etching treatment or a desmutting treatment is preferably carried out, and the alkali etching treatment and the desmutting treatment may also be preferably carried out in this order. The alkali etching treatment after the electrolytic surface-roughening treatment may be omitted. In the presently disclosed subject matter, before these treatments, a mechanical surface-roughening treatment may also be preferably carried out. The electrolytic surface-roughening treatment may be carried out two or more times. Further, after these treatments, an anodizing treatment, a sealing treatment, a hydrophilicizing treatment and the like may be preferably carried out.

Hereinafter, a mechanical surface-roughening treatment, a first alkali etching treatment, a first desmutting treatment, an electrolytic surface-roughening treatment, a second alkali etching treatment, a second desmutting treatment, an anodizing treatment, a sealing treatment and a hydrophilicizing treatment each will be described in detail. Here, in the present embodiment, treatments carried out before the electrolytic surface-roughening treatment may be referred to as with an ordinal number of “first”, and treatments carried out after the electrolytic surface-roughening treatment may be referred to as with an ordinal number of “second”.

<Mechanical Surface-Roughening Treatment>

The mechanical surface-roughening treatment is preferably carried out before the electrolytic surface-roughening treatment. The mechanical surface-roughening treatment is generally carried out by rubbing one or both of surfaces of the aluminum web by using a roller brush having a large number of brush bristles such as synthetic resin bristles composed of a synthetic resin such as nylon (registered trade mark of Japan), propylene or vinyl chloride resins implanted on the surface of a cylindrical drum while a slurry liquid containing an abrasive is being sprayed on the roller brush. In place of the roller brush and the slurry liquid, a grinding roller as a roller having a grinding layer provided on its surface may be used. The length of brush bristles of the roller brush can suitably be determined depending on the outer diameter of the roller brush and the diameter of the drum, but is generally 10 to 100 mm.

As the abrasive, following materials can be used. For example, abrasives such as pumice stone, quartz sand, aluminum hydroxide, alumina powder, volcanic ash, Carborundum and emery sand, or mixtures thereof can be used. Above all, pumice stone and quartz sand are preferable, but especially quartz sand is preferable from the viewpoint that the surface-roughening efficiency is excellent because quartz sand is harder and more hardly destroyed than pumice stone. The average particle diameter of an abrasive is preferably 3 to 50 μm, and more preferably 6 to 45 μm, from the viewpoint that the surface-roughening efficiency is excellent and sand dressing pitches can be narrowed. In the case of using pumice stone as the abrasive, the average particle diameter is especially preferably 40 to 45; and in the case of using quartz sand, the average particle diameter is especially preferably 20 to 25 μm. An abrasive is, for example, suspended in water and used as a grinding slurry liquid. The grinding slurry liquid may contain, in addition to the abrasive, a thickening agent, a dispersant (for example, a surfactant), an antiseptic agent, and the like. The average particle diameter refers to a particle diameter at which a cumulative proportion becomes 50% in a cumulative distribution of the proportion accounted for by abrasive particles of each particle diameter with respect to the volume of all the abrasives contained in the grinding slurry liquid.

In the mechanical surface-roughening treatment, prior to carrying out the brush graining, as required, a degreasing treatment to remove a rolling oil on the surface of the aluminum web may be carried out using, for example, a surfactant, an organic solvent, an alkali aqueous solution or the like.

<A First Alkali Etching Treatment>

A first alkali etching treatment brings the aluminum web into contact with an alkali solution to thereby carry out etching. The first alkali etching treatment is carried out, in the case where the mechanical surface-roughening treatment has not been carried out, in order to remove the rolling oil, fouling and a naturally oxidized film on the surface of the aluminum web (rolled aluminum), and in the case where the mechanical surface-roughening treatment has been carried out, in order to dissolve irregular edge portions generated in the mechanical surface-roughening treatment to make a surface having a smooth undulation. Examples of the method for bringing an aluminum web into contact with an alkali solution include a method in which the aluminum web is passed through in a bath containing the alkali solution, a method in which the aluminum web is immersed in a bath containing the alkali solution, and a method in which the alkali solution is sprayed on a surface of the aluminum web.

The etching amount is preferably 1 to 15 g/m² for the surface which is to be subjected to an electrolytic surface-roughening treatment in the successive step, and for the surface which is not to be subjected to the electrolytic surface-roughening treatment, preferably 0.1 to 5 g/m² (about 10 to 40% of the etching amount for the surface which is to be subjected to the electrolytic surface-roughening treatment).

Examples of alkalis used for the alkali solution include caustic alkalis and alkaline metal salts. Specific examples of the caustic alkalis include caustic soda and caustic potash. Examples of the alkaline metal salts include alkaline metal silicates such as soda metasilicate, soda silicate, potash metasilicate and potash silicate; alkaline metal carbonates such as soda carbonate and potash carbonate; alkaline metal aluminates such as soda aluminate and potash aluminate; alkaline metal aldonates such as soda gluconate and potash gluconate; and alkaline metal hydrogenphosphate salts such as dibasic soda phosphate, dibasic potash phosphate, tribasic soda phosphate and tribasic potash phosphate. Above all, a solution of a caustic alkali, and a solution containing both of a caustic alkali and an alkaline metal aluminate are preferable from the viewpoint that the etching rate is high and the alkali is inexpensive. Especially an aqueous solution of caustic soda is preferable.

The concentration of the alkali solution can be determined depending on the etching amount, but is preferably 1 to 50% by mass, and more preferably 10 to 35% by mass. In the case where aluminum ions are dissolved in the alkali solution, the concentration of aluminum ions is preferably 0.01 to 10% by mass, and more preferably 3 to 8% by mass. The temperature of the alkali solution is preferably 20 to 90° C. The treatment time is preferably 1 to 120 sec. The etching treatment amount is preferably a dissolution of 1 to 15 g/m², and more preferably a dissolution of 3 to 12 g/m². The first alkali etching treatment can be carried out using an etching bath used usually for the etching treatment of an aluminum web. As the etching bath, either of a batch type and a continuous type may be used. In the case where the first alkali etching treatment is carried out by spraying an alkali solution on a surface of an aluminum web, a spray apparatus can be used.

<A First Desmutting Treatment>

A first desmutting treatment is carried out, for example, by bringing the aluminum web into contact with an acidic solution (containing 0.01 to 5% by mass of aluminum ions) of 0.5 to 30% by mass in concentration such as hydrochloric acid, nitric acid or sulfuric acid. Examples of a method of bringing an aluminum web into contact with an acidic solution include a method in which the aluminum web is passed through in a bath containing the acidic solution, a method in which the aluminum web is immersed in a bath containing the acidic solution, and a method in which the acidic solution is sprayed on a surface of the aluminum web. In the first desmutting treatment, as the acidic solution, preferably used are a waste solution of an aqueous solution discharged in an electrolytic surface-roughening treatment described later and containing nitric acid as a main component, or of an aqueous solution discharged therein and containing hydrochloric acid as a main component, or a waste solution of an aqueous solution discharged in an anodizing treatment described later and containing sulfuric acid as a main component. The liquid temperature of the first desmutting treatment is preferably 25 to 90° C. The treatment time of the first desmutting treatment is preferably 1 to 180 sec.

<Electrolytic Surface-Roughening Treatment>

Here, an electrolytic surface-roughening treatment is carried out by applying the electrolytic surface-roughening treatment apparatus 10 according to the presently disclosed subject matter.

An acidic aqueous solution used in an electrolytic surface-roughening treatment is not especially limited, but is preferably an aqueous solution containing nitric acid as a main component, and an aqueous solution containing hydrochloric acid as a main component. The nitric acid concentration of the aqueous solution containing nitric acid as a main component is preferably 3 to 20 g/L, and more preferably 5 to 15 g/L; and the aluminum ion concentration is preferably 3 to 15 g/L, and more preferably 3 to 7 g/L. The concentration of aluminum ions in the aqueous solution containing nitric acid as a main component can be regulated by adding aluminum nitrate to the nitric acid aqueous solution of the above-mentioned nitric acid concentration. The hydrochloric acid concentration of the aqueous solution containing hydrochloric acid as a main component is preferably 3 to 15 g/L, and more preferably 5 to 10 g/L; and the aluminum ion concentration is preferably 3 to 15 g/L, and more preferably 3 to 7 g/L. The concentration of aluminum ions in the aqueous solution containing hydrochloric acid as a main component can be regulated by adding aluminum chloride to the hydrochloric acid aqueous solution of the above-mentioned hydrochloric acid concentration.

<A Second Alkali Etching Treatment>

A second alkali etching treatment brings the aluminum web into contact with an alkali solution to thereby carry out etching. The type of alkali, the method of bringing the aluminum web into contact with an alkali solution and the apparatus used for the method include the same ones as in the case of the first alkali etching treatment. The etching amount is, for the surface which has been subjected to the electrolytic surface-roughening treatment, preferably 0.001 to 5 g/m², more preferably 0.01 to 3 g/m², and still more preferably 0.05 to 2 g/m².

The alkali used for the alkali solution includes the same one as in the case of the first alkali etching treatment. The concentration of the alkali solution can be determined depending on the etching amount, but is preferably 0.01 to 80% by mass. The temperature of the alkali solution is preferably 20 to 90° C. The treatment time is preferably 1 to 60 sec. In the case where in a second desmutting treatment described later, an acidic solution is used in which 100 g/L or more of sulfuric acid is contained and the liquid temperature is 60° C. or higher, the second alkali etching treatment may be omitted.

<A Second Desmutting Treatment>

A second desmutting treatment is carried out, for example, by bringing the aluminum web into contact with an acidic solution (containing 0.01 to 5% by mass of aluminum ions) of 0.5 to 30% by mass in concentration such as phosphoric acid, hydrochloric acid, nitric acid or sulfuric acid. The method of bringing the aluminum web into contact with an acidic solution includes the same one as in the case of the first desmutting treatment. As an acidic solution in the second desmutting treatment, preferably used is a waste solution of a sulfuric acid solution discharged in an anodizing treatment described later. In place of the waste solution, a sulfuric acid solution may be used in which the sulfuric acid concentration is 100 to 600 g/L; the aluminum ion concentration is 1 to 10 g/L; and the liquid temperature is 60 to 90° C. The liquid temperature of the second desmutting treatment is preferably 25 to 90° C. The treatment time of the second desmutting treatment is preferably 1 to 180 sec. In an acidic solution used for the second desmutting treatment, aluminum and aluminum alloy components may be dissolved.

<Anodizing Treatment>

The aluminum web having been treated as described above is preferably further subjected to an anodizing treatment. The anodizing treatment can be carried out by a method conventional in this field. Specifically, an anodic oxide film can be formed on a surface of an aluminum web by making a direct current, a pulsating current or an alternating current flow to the aluminum web in an aqueous solution of sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, amidosulfonic acid or the like singly or in combination of two or more thereof, or an electrolytic solution as a nonaqueous solution.

Among these electrolytic solutions, a sulfuric acid solution is preferably used as an electrolytic solution. The sulfuric acid concentration in the electrolytic solution is preferably 10 to 300 g/L (1 to 30% by mass); and the aluminum ion concentration is preferably 1 to 25 g/L (0.1 to 2.5% by mass), and more preferably 2 to 10 g/L (0.2 to 1% by mass). Such an electrolytic solution can be prepared, for example, by adding aluminum to a dilute sulfuric acid of 50 to 200 g/L in sulfuric acid concentration.

In the case where the anodizing treatment is carried out in an electrolytic solution containing sulfuric acid, a direct current may be applied to an aluminum web, or an alternating current may be applied thereto. In the case where a direct current is applied to the aluminum web, the current density is preferably 1 to 60 A/dm², and more preferably 5 to 40 A/dm². In the case where the anodizing treatment is carried out continuously, it is preferable that a current of a low current density of 5 to 10 A/dm² is made to flow at the initiation of the anodizing treatment so as not to concentrate the current on a part of the aluminum web, and as the anodizing treatment proceeds, the current density is increased to 30 to 50 A/dm² or more. In the case where the anodizing treatment is carried out continuously, the power feeding is preferably carried out by a through-liquid power feeding system to feed a power to the aluminum web through an electrolytic solution.

As an electrode to feed a power to an aluminum web, an electrode formed from lead, iridium oxide, platinum, a ferrite or the like can be used. Above all, an electrode formed from iridium oxide, and an electrode in which the surface of a base material is coated with iridium oxide are preferable. As such a base material, a so-called valve metal such as titanium, tantalum, niobium or zirconium is preferably used, and among the valve metals, titanium and niobium are preferable. Since the valve metals have a relatively large electric resistance, the surface of a core material composed of copper may be clad with a valve metal to form a base material. In the case where the surface of a core material composed of copper is clad with a valve metal, since it is difficult to fabricate a complicate-shape base material, core materials in a form in which the base material is divided into components may be each clad with a valve metal, and thereafter, the components may be combined to assemble the base material.

The conditions of the anodizing treatment cannot be determined unconditionally because they variously varies depending on an electrolytic solution to be used, but are generally suitably: the electrolytic solution concentration is 1 to 80% by mass; the liquid temperature is 5 to 70° C.; the current density is 1 to 60 A/dm²; the voltage is 1 to 100 V; and the electrolysis time is 10 to 300 sec. It is preferable from the viewpoint of the printing durability of a planographic printing plate that the anodizing treatment is carried out so that the amount of an anodic oxide film becomes 1 to 5 g/m². Additionally, the anodizing treatment is preferably carried out so that the difference in the amount of the anodic oxide film between the center part and edge vicinities of the aluminum web is 1 g/m² or less.

<Sealing Treatment>

An aluminum alloy plate on which an anodic oxide film has been formed is brought into contact with boiled water, hot water or steam preferably to carry out a sealing treatment in which micropores present in the anodizing treatment are sealed.

<Hydrophilicizing Treatment>

After the anodizing treatment or the sealing treatment, a hydrophilicizing treatment is preferably carried out by a method in which the resulting aluminum web is immersed in an aqueous solution of an alkaline metal silicate such as soda silicate or potash silicate, a method in which the resulting aluminum web is coated with a hydrophilic vinyl polymer or a hydrophilic compound to form a hydrophilic undercoat layer, or another method. Examples of the hydrophilic vinyl polymer used in this method include polyvinylsulfonic acids and copolymers of a sulfonic acid group-containing vinyl-polymerizable compound having a sulfonic acid group such as p-styrenesulfonic acid and a usual vinyl-polymerizable compound such as an alkyl (meth)acrylate. Examples of the hydrophilic compound used in this method include compounds having at least one selected from the group consisting of amino (—NH₂) group, carboxyl (—COOH) group and a sulfo group.

<An Intermediate Layer>

Although a photosensitive layer may be provided directly on the support for a planographic printing plate having been subjected to the hydrophilicizing treatment, or on the support for a planographic printing plate having been further subjected to an acidic aqueous solution treatment after the hydrophilicizing treatment, as required, an intermediate layer may be provided on the support and a photosensitive layer may be provided on the intermediate layer.

(An Intermediate Layer of a Polymeric Compound Having an Acid Group and an Onium Group)

As a polymeric compound to be used for forming an intermediate layer, more suitably used is a polymeric compound having an acid group or having a constituting component having an acid group and also a constituting component having an onium group. The acid group of the constituting component of the polymeric compound is preferably an acid group having an acid dissociation exponent (pKa) of 7 or less, more preferably —COOH, —SO₃H, —OSO₃H, —PO₃H₂, —OPO₃H₂, —CONHSO₂ and —SO₂NHSO₂—, and especially preferably —COOH. A suitable constituting component having an acid group is a polymerizable compound represented by the general formula (1) or (2) illustrated below.

In the formulae, A denotes a divalent linking group; B denotes an aromatic group or a substituted aromatic group; D and E each independently denote a divalent linking group; G denotes a trivalent linking group; X and X′ each independently denote an acid group having a pKa of 7 or less, an alkaline metal salt thereof or an ammonium salt thereof; R₁ denotes a hydrogen atom, an alkyl group or a halogen atom; a, b, d and e each independently denote 0 or 1; and t is an integer of 1 to 3. In a more preferable constituting component having an acid group, A denotes —COO— or CONH—; B denotes a phenylene group or a substituted phenylene group, wherein the substituent is a hydroxyl group, a halogen group (halogen atom) or an alkyl group; D and E each independently denote an alkylene group or a divalent linking group whose molecular formula is represented by C_(n)H_(2n)O, C_(n)H_(2n)S or C_(n)H_(2n+1)N; G denotes a trivalent linking group whose molecular formula is represented by C_(n)H_(2n−1), C_(n)H_(2n−1)O, C_(n)H_(2n−1)S or C_(n)H_(2n)N, wherein n denotes an integer of 1 to 12; X and X′ each independently denote a carboxylic acid, a sulfonic acid, a phosphonic acid, a sulfuric acid monoester or a phosphoric acid monoester; R₁ denotes a hydrogen atom or an alkyl group; and a, b, d and e each independently denote 0 or 1, but a and b are not 0 at the same time. An especially preferable constituting component having an acid group is a compound represented by the general formula (1) wherein, B denotes a phenylene group or a substituted phenylene group wherein the substituent is a hydroxyl group or an alkyl group having 1 to 3 carbon atoms; D and E each independently denote an alkylene group having 1 to 2 carbon atoms, or alkylene groups having 1 to 2 carbon atoms linked with an oxygen atom; R₁ denotes a hydrogen atom or a methyl group; X denotes a carboxylic acid group; and a is 0, and b is 1.

Specific examples of the constituting component having an acid group are illustrated below, but the components are not especially limited thereto, and the components can include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, itaconic acid, maleic acid and maleic anhydride, and further include the following.

The constituting component having an acid group as illustrated above may be used singly or in combination of two or more.

(An Intermediate Layer of a Polymeric Compound Having an Onium Group)

A preferable onium group of a constituting component of a polymeric compound used for forming the intermediate layer is preferably an onium group including an atom of Group V or VI in the periodic table, and is more preferably an onium group including a nitrogen atom, a phosphorus atom or a sulfur atom, and especially preferably an onium group including a nitrogen atom. The polymeric compound is preferably a polymer whose main chain structure is a vinylic polymer such as an acryl resin, a methacryl resin or a polystyrene, or a urethane resin, a polyester or a polyamide. Above all, a vinylic polymer is more preferable whose main chain structure is an acryl resin, a methacryl resin or a polystyrene. An especially preferable polymeric compound is a polymer as a polymerizable compound in which the constituting component having an onium group is represented by the general formula (3), the general formula (4) or the general formula (5) illustrated below.

In the formulae, J denotes a divalent linking group; K denotes an aromatic group or a substituted aromatic group; M each independently denote a divalent linking group; Y₁ denotes an atom of Group V of the periodic table, and Y₂ denotes an atom of Group VI of the periodic table; Z⁻ denotes a counter anion; R₂ denotes a hydrogen atom, an alkyl group or a halogen atom; R₃, R₄, R₅ and R₇ each independently denote a hydrogen atom, or an alkyl group, an aromatic group or an aralkyl group which may be bonded with a substituent as required, R₆ denotes an alkylidyne or a substituted alkylidyne, and R₃ and R₄, and R₆ and R₇ may each bond to form a ring; and j, k and m each independently denote 0 or 1, and u denotes an integer of 1 to 3. In a more preferable constituting component having an onium group, J denotes —COO— or CONH—; K denotes a phenylene group or a substituted phenylene group, wherein the substituent is a hydroxyl group, a halogen atom or an alkyl group; M denotes an alkylene group or a divalent linking group whose molecular formula is represented by C_(n)H_(2n)O, C_(n)H_(2n)S or C_(n)H_(2n+1)N, wherein n denotes an integer of 1 to 12; Y₁ denotes a nitrogen atom or a phosphorus atom; Y₂ denotes a sulfur atom; Z⁻ denotes a halogen ion, PF₆ ⁻, BF₄ ⁻ or R₈SO₃ ⁻; R₂ denotes a hydrogen atom or an alkyl group, R₃, R₄, R₅ and R₇ each independently denote a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, an aromatic group or an aralkyl group which may be bonded with a substituent as required, and R₆ denotes an alkylidyne group having 1 to 10 carbon atoms or a substituted alkylidyne group, but R₃ and R₄, and R₆ and R₇ may each bond to form a ring; and j, k and m each independently denote 0 or 1, but j and k are not 0 at the same time. In an especially preferable constituting component having an onium group, K denotes a phenylene group or a substituted phenylene group, wherein the substituent is a hydroxyl group or an alkyl group having 1 to 3 carbon atoms; M denotes an alkylene group having 1 to 2 carbon atoms or alkylene groups having 1 to 2 carbon atoms linked with an oxygen atom; Z⁻ denotes a chlorine ion or R₈SO₃ ⁻; R₂ denotes a hydrogen atom or a methyl group; and j is 0, and k is 1.

<A Photosensitive Layer>

A planographic printing original plate can be obtained by providing a photosensitive layer on a support for a planographic printing plate before an intermediate layer is formed thereon, or a support for a planographic printing plate on which an intermediate layer has been formed.

The photosensitive layer is not especially limited, but examples thereof include a visible light exposure-type plate making layer to be exposed with visible light, and a laser exposure-type plate making layer to be exposed with laser light such as infrared laser light. Hereinafter, the visible light exposure-type plate making layer and the laser exposure-type plate making layer will be described.

(1) A Visible Light Exposure-Type Plate Making Layer

A visible light exposure-type plate making layer can be formed from a composition containing a photosensitive resin and as required, a colorant and the like. The photosensitive resin includes a positive-type photosensitive resin which comes to dissolve in a developing solution when light is irradiated, and a negative-type photosensitive resin which comes not to dissolve in a developing solution when light is irradiated. Examples of the positive-type photosensitive resin include combinations of a diazide compound such as a quinone diazide compound or a naphthoquinone diazide compound and a phenol resin such as a phenol novolac resin or a cresol novolac resin. Examples of the negative-type photosensitive resin include combinations of a diazo compound such as a diazo resin (for example, condensates of an aromatic diazonium salt and an aldehyde such as formaldehyde), an inorganic salt of the diazo resin or an organic salt of the diazo resin and a binding agent such as a (meth)acrylate resin, a polyamide resin or a polyurethane resin, and combinations of a vinyl polymer such as a (meth)acrylate resin or a polystyrene resin, a vinyl-polymerizable compound such as a (meth)acrylate ester or styrene and a photopolymerization initiator such as a benzoin derivative, a benzophenone derivative or a thioxanthone derivative.

As the colorant, other than usual dyes, usable are exposure color-forming dyes to form a color by exposure, exposure color-fading dyes which become almost or completely colorless by exposure, and the like. Examples of the exposure color-forming dye include leuco dyes. Examples of the exposure color-fading dye include triphenylmethane-based dyes, diphenylmethane-based dyes, oxazine-based dyes, xanthene-based dyes, aminonaphthoquinone-based dyes, azomethine-based dyes and anthraquinone-based dyes.

The visible light exposure-type plate making layer can be formed, for example, by applying a photosensitive resin solution in which the photosensitive resin, the colorant and a solvent are blended, and thereafter drying the solution. The solvent used for the photosensitive resin solution includes solvents which can dissolve the photosensitive resin and have a volatility of some degree at room temperature. Specific examples thereof include alcoholic solvents, ketone solvents, esteric solvents, etheric solvents, glycol ether solvents, amido solvents and carbonate solvents. Examples of the alcoholic solvents include ethanol, propanol and butanol. Examples of the ketone solvents include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone and diethyl ketone. Examples of the esteric solvents include ethyl acetate, propyl acetate, methyl formate and ethyl formate. Examples of the etheric solvents include tetrahydrofuran and dioxane. Examples of the glycol ether solvents include ethyl cellosolve, methyl cellosolve and butyl cellosolve. Examples of the amide solvents include dimethylformamide and dimethylacetamide. Examples of the carbonate solvents include ethylene carbonate, propylene carbonate, diethyl carbonate and dibutyl carbonate.

A method for coating the photosensitive resin solution is not especially limited, and, for example, the rotary coating method, the wire-bar coating method, the dip coating method, the air-knife coating method, the roll coating method and the blade coating method can be used.

(2) A Laser Exposure-Type Plate Making Layer

Examples of the laser exposure-type plate making layer include a negative-type laser plate making layer in which portions irradiated with a laser light remain, a positive-type laser plate making layer in which portions irradiated with a laser light are removed, and a photopolymerization-type plate making layer in which the irradiation with a laser light carries out the photopolymerization.

A negative-type laser plate making layer can be formed by using a solution for forming the negative-type laser plate making layer, in which solution (A) an acid precursor which decomposes by heat or light to generate an acid, (B) an acid-crosslinkable compound which crosslinks by the acid generated by the decomposition of the acid precursor (A), (C) an alkali-soluble resin, (D) an infrared absorbent, and (E) a phenolic hydroxyl group-containing compound are dissolved or suspended in an appropriate solvent.

Examples of the acid precursor (A) include compounds to decompose by ultraviolet light, visible light or heat to generate sulfonic acid, like iminophosphate compounds. Additionally, compounds being generally used as cationic photopolymerization initiators, radical photopolymerization initiators, photodiscoloring agents and the like can be used as the acid precursor (A). Examples of the acid-crosslinkable compound (B) include aromatic compounds having at least one of an alkoxymethyl group and a hydroxyl group, compounds having an N-hydroxymethyl group, an N-alkoxymethyl group or an N-acyloxymethyl group, and epoxy compounds. Examples of the alkali-soluble resin (C) include polymers in which the side chains of a novolac resin, a poly(hydroxystyrene) or the like have a hydroxyaryl group.

Examples of the infrared absorbent (D) include dyestuffs and pigments to absorb infrared rays of 760 to 1,200 nm in wavelength. Specific examples thereof include black pigments, red pigments, metal powder pigments and phthalocyanine-based pigments; and azo dyestuffs, anthraquinone dyestuffs, phthalocyanine dyestuffs and cyanine dyes which absorb infrared rays of the above-mentioned wavelength. Examples of the phenolic hydroxyl group-containing compound (E) include compounds represented by the general formula (R₁—X)_(n)—Ar—(OH)_(m) (wherein R₁ is an alkyl group or an alkenyl group having 6 to 32 carbon atoms; X is a single bond, O, S, COO or CONH; Ar is an aromatic hydrocarbon group, an alicyclic hydrocarbon group or a heterocyclic group; and n and m are each a natural number of 1 to 8). Examples of such compounds include alkylphenols such as nonylphenol. A plasticizer and the like can be blended in the solution for forming a negative-type laser plate making layer in addition to the above-mentioned components.

A positive-type laser plate making layer can be formed by using a solution for forming the positive-type laser plate making layer, in which solution (F) an alkali-soluble polymer, (G) an alkali-dissolution inhibitor, and (H) an infrared absorbent are dissolved or suspended in an appropriate solvent. Examples of the alkali-soluble polymer (F) include phenolic polymers having a phenolic hydroxyl group, such as phenol resins, cresol resins, novolac resins, pyrogallol resins and poly(hydroxystyrene); sulfonamide group-containing polymers as polymers in which at least a part of monomer units has a sulfonamide group; and active imide group-containing polymers obtained by homopolymerizing or copolymerizing a monomer having an active imide group such as N-(p-toluenesulfonyl)(meth)acrylamide group.

Examples of the alkali-dissolution inhibitor (G) include compounds which react with an alkali-soluble polymer (F) by heating or otherwise to decrease the solubility of the alkali-soluble polymer (F) to an alkali. Specific examples thereof include sulfone compounds, ammonium salts, sulfonium salts and amide compounds. A combination of an alkali-soluble polymer (F) and an alkali-dissolution inhibitor (G) suitably includes a combination of a novolac resin as the alkali-soluble polymer (F) and a cyanine dye as one type of sulfone compounds as the alkali-dissolution inhibitor (G). Examples of the infrared absorbent (H) include dyes, dyestuffs and pigments which have an infrared absorption region of 750 to 1,200 nm in wavelength and have a photo-thermal conversion function, such as squalirium dyes, pyrylium dyes, carbon black, insoluble azo dyestuffs and anthraquinone-based dyestuffs.

The photopolymerization-type laser plate making layer can be formed by using a solution for forming the photopolymerization-type laser plate making layer, which solution contains (I) a vinyl-polymerizable compound having an ethylenic unsaturated bond at a molecular terminal thereof. In a solution for forming a photopolymerization-type laser plate making layer, as required, (J) a photopolymerization initiator, (K) a sensitizer and the like can be blended. Examples of the vinyl-polymerizable compound (I) include ethylenic unsaturated carboxylic acid polyvalent esters which are esters of an ethylenic unsaturated carboxylic acid, such as (meth)acrylic acid, itaconic acid or maleic acid, and an aliphatic polyhydric alcohol; methylenebis(meth)acrylamides having the ethylenic unsaturated carboxylic acid and a polyvalent amine; and ethylenic unsaturated carboxylic acid polyvalent amides such as xylylene(meth)acrylamide. The vinyl-polymerizable compound (I) additionally includes aromatic vinyl compounds such as styrene and α-methylstyrene; and ethylenic unsaturated carboxylic acid monoesters such as methyl (meth)acrylate and ethyl (meth)acrylate. As the photopolymerization initiator (J), photopolymerization initiators usually used in the photopolymerization of vinylic monomers can be used. Examples of the sensitizer (K) include titanocene compounds, triazine compounds, benzophenone-based compounds, benzimidazole-based compounds, cyanine dyes, merocyanine dyes, xanthene dyes and coumarin dyes.

As solvents used for a solution for forming the negative-type laser plate making layer, a solution for forming the positive-type plate making layer and a solution for forming the photopolymerization-type laser plate making layer, as described above, and as methods for coating the solution for forming the negative-type laser plate making layer, the solution for forming the positive-type plate making layer and the solution for forming the photopolymerization-type laser plate making layer, the solvent and the coating method used for the photosensitive resin solution described above can be used. Here, in the case of forming a photopolymerization-type laser plate making layer, if a surface of a support for a planographic printing plate to be subjected to a surface-roughening treatment is previously treated with a silicone compound having a reactive functional group such as a partially decomposed-type silane compound obtained by partially decompose a silane compound with a water, an alcohol or a carboxylic acid, the adhesivity between the support and the photopolymerization-type laser plate making layer is improved, which is preferable.

<A Mat Layer>

A mat layer may be provided on the surface of the photosensitive layer provided as described above in order to reduce the vacuuming time when a contact exposure using a vacuum printing frame and to prevent print blur. A method for providing a mat layer specifically includes a method for providing a mat layer as described in Japanese Patent Application Laid-Open No. 50-125805 and Japanese Examined Application Publication Nos. 57-6582 and 61-28986, and a method in which a solid powder is thermally vapor-deposited as described in Japanese Examined Application Publication No. 62-62337.

<A Backcoat Layer>

A coating layer (hereinafter, also referred to as “backcoat layer”) having an organic polymeric compound may be provided as required on the back surface (the surface of the side on which the photosensitive layer is not provided) of a planographic printing original plate obtained as described above so that the planographic printing original plate is not scratched when stacked. As the main component of the backcoat layer, preferably used is at least one selected from the group consisting of saturated copolymerized polyester resins, phenoxy resins, polyvinyl acetal resins and vinylidene chloride copolymerized resins whose glass transition temperatures are 20° C. or higher.

The saturated copolymerized polyester resin is composed of a dicarboxylic acid unit and a diol unit. Examples of the dicarboxylic acid unit include aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, tetrabromophthalic acid and tetrachlorophthalic acid; and saturated aliphatic dicarboxylic acids such as adipic acid, azelaic acid, succinic acid, oxalic acid, suberic acid, sebacic acid, malonic acid and 1,4-cyclohexanedicarboxylic acid.

The backcoat layer may suitably contain further a dyestuff or pigment for coloring, a silane coupling agent, a diazo resin containing a diazonium salt, an organophosphonic acid, an organophosphoric acid and a cationic polymer which improve contact adhesivity with a support, and a wax, a higher fatty acid, a higher fatty amide, a silicone compound containing dimethylsiloxane, a modified dimethylsiloxane and a polyethylene powder which are usually used as a lubricant, and the like.

The thickness of the backcoat layer may be one at a level at which a photosensitive layer is hardly scratched without an inserting paper, and is preferably 0.01 to 8 μm. If the thickness is less than 0.01 μm, it is difficult to prevent rubbing scratches on the photosensitive layer when the planographic printing original plate is stackingly handled. By contrast, if the thickness exceeds 8 μm, the backcoat layer swells and varies the thickness due to chemicals used in the vicinity of the planographic printing plate during printing, and the printing pressure varies and printing characteristics deteriorate in some cases.

As a method for providing a backcoat layer on the back surface of a planographic printing original plate, various types of methods can be used. Examples thereof include a method in which components for the backcoat layer are dissolved in an appropriate solvent to make a solution, which is then coated, or to make an emulsified dispersion, which is applied, and the solution or the dispersion is dried; a method in which a backcoat layer previously formed into a film form is pasted on a planographic printing original plate by using an adhesive or heat; and a method in which a melted film is formed by a melt extruder, and pasted on a planographic printing original plate. The most preferable method is, in order to secure a suitable thickness, the method in which components for the backcoat layer are dissolved in an appropriate solvent to make a solution, which is then coated, and dried.

In manufacture of a planographic printing original plate, whichever may be first provided on a support, the backcoat layer on the back surface or the photosensitive layer on the front surface; or the both may be provided simultaneously.

The planographic printing original plate thus obtained is, as required, cut into an appropriate size, and exposed and developed to obtain a planographic printing plate. In the case of a planographic printing original plate provided with a visible light exposure-type plate making layer (photosensitive plate making layer), a transparent film on which printing images are formed is stacked, and the plate making layer is irradiated with a visible light to be exposed, and thereafter, developed to make a printing plate. In the case of a planographic printing original plate provided with a laser exposure-type plate making layer, the plate making layer is irradiated with various types of laser rays to directly write printing images to be exposed, and thereafter, developed to make a printing plate.

Hitherto, examples of applying the presently disclosed subject matter to the manufacturing method of a support for a planographic printing plate have been described, but the presently disclosed subject matter can be applied to other technical fields in which a step of subjecting a surface of a metal plate to which the presently disclosed subject matter is applicable to an electrolytic surface-roughening treatment is provided.

Examples

Then, the presently disclosed subject matter will be described in detail by way of Examples, but the presently disclosed subject matter is not limited to the following Examples.

By using an electrolytic surface-roughening treatment apparatus 10 illustrated in FIG. 1, an electrolytic surface-roughening treatment was carried out on an aluminum web W of 300 mm in width and 0.2 mm in thickness. As an electrolytic surface-roughening treatment condition, L.S. (line speed) was set at 100 m/min. For Examples 1 to 6, the inter-electrode distance L between the aluminum web W and a direct current unit was set at 10 mm. The time from a pretreatment step to an alternating current treatment step was set at 5 sec or less.

The quality of the aluminum web W electrolytically surface-roughened in the electrolytic surface-roughening treatment apparatus 10 was evaluated visually for the presence/absence of chatter marks.

The evaluation level was graded as the following five-stage evaluation, and B or higher was considered to be a passing grade.

A . . . A very large improving effect on chatter marks (The suppressing effect on the generation of chatter marks is larger than “B to A”.).

B to A . . . A sufficiently improving effect on chatter marks (The suppressing effect on the generation of chatter marks is larger than “B” and is smaller than “A”.).

B . . . An improving effect on chatter marks (The suppressing effect on the generation of chatter marks is larger than “C to B” and is smaller than “B to A”.).

C to B . . . An insufficiently improving effect on chatter marks (The suppressing effect on the generation of chatter marks is larger than “C” and is smaller than “B”.).

C . . . No improving effect on chatter marks (The suppressing effect on the generation of chatter marks is smaller than “C to B”.).

[Test Results]

Test results are illustrated in Table in FIG. 5.

As illustrated in Table in FIG. 5, in Examples 1 to 6 in which a direct current unit 26 was installed in an electrolytic bath 12A and at an inter-electrode distance L of 10 mm from the aluminum web W, and a negative direct-current voltage was applied to the aluminum web W, the evaluations of chatter marks were B or higher. That is, it was recognized that Examples 1 to 6 in which hydroxide ions were made to be distributed on a surface of the aluminum web W before carrying out the alternating current electrolytic treatment exhibited a sufficiently suppressing effect on chatter marks. Thereby, it was demonstrated that holes uniform in size could be formed on portions of the aluminum web W where the alternating current electrolytic treatment was initiated from an anodic reaction when the aluminum web W was continuously subjected to the alternating current electrolytic treatment with an alternating waveform current while being transported in an acidic electrolytic solution, and the generation of chatter marks could thus be effectively suppressed.

Particularly, as is clear from the results of Examples 1 to 3, by changing the current density to a lower one successively from −10 A/dm² to −50 A/dm² (the absolute value became larger successively), the evaluations of chatter marks became better successively. As is clear from this result, the sufficient distribution of hydroxide ions on the aluminum web W in the pretreatment step contributed to the suppression of chatter marks.

By contrast, in Comparative Example 1 in which the electrolytic surface-roughening treatment apparatus 10 installed with no direct current unit 26 was used, no improving effect on chatter marks was exhibited at all (The evaluation level of Comparative Example 1 is “C”). In Comparative Example 2 in which before an alternating current electrolytic treatment, a positive direct-current voltage was applied to a surface of the aluminum web W to carry out an anodic reaction, the generation of chatter marks were suppressed more than in Comparative Example 1 in which on direct current unit 26 was installed, but the suppression was insufficient (The evaluation level of Comparative Example 2 is “C to B”). In Comparative Example 3 in which although before the alternating current electrolytic treatment, a negative direct-current voltage was applied on a surface of the aluminum web W to carry out a cathodic reaction, the pretreatment was carried out in a bath different from an electrolytic bath body where an alternating current electrolysis was carried out, the evaluation of chatter marks was C to B, exhibiting an insufficiently improving effect on chatter marks.

As is clear from the comparison of Example 1 with Comparative Example 4, even in the case where before the alternating current electrolytic treatment, a negative direct-current voltage was applied on a surface of the aluminum web W to carry out a cathodic reaction, if the inter-electrode distance exceeded 10 mm and was separated to 20 mm, the improving effect on chatter marks was insufficient. 

1. An electrolytic treatment method comprising continuously subjecting a strip-shaped metal plate to an alternating current electrolytic treatment with an alternating waveform current in an acidic electrolytic solution while transporting the metal plate therein; and before the alternating current electrolytic treatment, carrying out a pretreatment step of previously adding hydroxide ions (OH⁻) on a surface of the metal plate.
 2. The electrolytic treatment method according to claim 1, further comprising applying a negative direct current voltage to the metal plate at an inter-electrode distance of 5 to 15 mm to carry out a cathodic reaction in an electrolytic bath in which the alternating current electrolytic treatment is carried out, to form the hydroxide ions.
 3. The electrolytic treatment method according to claim 2, wherein the cathodic reaction uses a current density of −10 A/dm² or lower.
 4. The electrolytic treatment method according to claim 1, wherein a time interval from at an end of the pretreatment step to at a start of the alternating current electrolytic treatment is 5 sec or less.
 5. An electrolytic treatment apparatus comprising: a transportation device configured to transport a metal plate; an electrolytic bath configured to store an acidic electrolytic solution, wherein the metal plate is transported inside the electrolytic bath; a current supplying device configured to supply an alternating waveform current to continuously subject a surface of the metal plate to an alternating current electrolytic treatment with the alternating waveform current; and a hydroxide ion-adding device installed in an inlet of the electrolytic bath through which the metal plate is introduced into the electrolytic bath, the hydroxide ion-adding device configured to add hydroxide ions (OH⁻) on a surface of the metal plate before the surface of the metal plate is subjected to the alternating current electrolytic treatment.
 6. The electrolytic treatment apparatus according to claim 5, wherein the hydroxide ion-adding device is a direct current unit installed in the electrolytic bath and at an inter-electrode distance of 5 to 15 mm from the metal plate, the direct current unit configured to apply a negative direct-current voltage to the metal plate.
 7. A method for manufacturing a planographic printing plate, the method comprising an electrolytic surface-roughening treatment step of electrolytically surface-roughening an aluminum plate, wherein the electrolytic surface-roughening treatment step includes an electrolytic treatment method according to claim
 1. 8. An apparatus for manufacturing a planographic printing plate, the apparatus comprising an electrolytic surface-roughening treatment apparatus to electrolytically surface-roughen an aluminum plate, wherein the electrolytic surface-roughening treatment apparatus includes an electrolytic treatment apparatus according to claim
 5. 